Reinforcement mats are used in many industries for adding strength to composite materials. Such mats are, in fact, generally referred to as composite reinforcements.
The reinforcement mats are typically formed in a location that is remote from place and time to the use of the reinforcement mat. As such, it is necessary to maintain the fibers of the mat in a predetermined configuration from the point of manufacture until the time of use. Typically, the reinforcement mats are stitched together or adhesively secured together to maintain the fibers in position. Although the use of stitching is generally effective to holding the fibers together, the stitching has some play, thus enabling the fibers to shift during transport of the reenforced mat, thus potentially compromising the strength and/or rigidity of the reinforcement mat. Stitching of the fibers together inherently provides relatively large loops or other closed circuits of the stitching. When reinforcing mats are stitched together in the manner known in the prior art, any activity which causes breaks in the stitching or pulls the stitching out of place can result in an undesired disruption of the fiber matrix which the stitching has created. For example, cutting the reinforcement mat, snagging the stitching and the like, can result in “unzipping” the stitching, thereby destroying the predetermined fiber orientation on the reinforcement mat. Likewise, when the reinforcement mat is cut into sections for use in a particular application, the stitching is severed at the ends of the reinforcement mat and can result in the “unzipping” of the stitching. In order to address these problems, the stitching thread can be melted-onto the fibers of the reinforcement mat to lock the fibers in place. An example of such a mat is disclosed in Bruner U.S. Pat. No. 5,795,835. Although the locking of the fibers by melting of the stitching thread maintains the fibers in rigid place with respect to one another, the flexibility of the reinforcement mat is significantly reduced. In many applications, the reinforcement mat is wrapped about a structure (e.g., pole, column, etc.) to provide support and/or strength to such structure. When the stitching on the reinforcement mat is melted onto the fibers, the stitching is susceptible to breaking when the reinforcement mat is wrapped about a structure. The breaking of the stitching can compromise the strength and durability of the reinforcement mat. Similarly, when the fibers are connected together by an adhesive, the bending of the reinforcement mat can cause the adhesive to break and/or release from the fibers thereby compromising the strength and durability of the reinforcement mat.
When reinforcement mats are impregnated with a liquid material, the adhesive on the reinforcement mat is susceptible to softening or dissolving, thereby compromising the strength and durability of the reinforcement mat. The softening or dissolving of the adhesive can also result in the movement of the fibers during the impregnation process, thereby potentially compromising the strength, durability and/or quality of the final product. In addition, certain adhesives can adversely affect the ability of the impregnating liquid to fully wet and saturate the fibers in the reinforcement mat thereby adversely affecting the strength, durability and/or quality of the final product. Furthermore, the impregnation process generally works best when the fibers on the reinforcement mat are held together in only a proximal relationship, but are not affixed to one another, to allow the penetration of the impregnating liquid about the fibers.
In an effort to address the past problems of reinforcement mats, a new type of reinforcement mat disclosed in WO 02/04725 was developed, which is incorporated herein by reference. The reinforcement mat was designed to be useful in the formation of reinforcing composite materials. The reinforcement mat is formed of at least first and second sets of fibers wherein the first set of fibers is laid as a ply in spaced apart parallel relationship in the direction of construction and the second set of fibers are laid as a ply in spaced apart parallel relationship which is perpendicular to the direction of construction. These two sets of fibers define interstices into which a continuous filament is knitted to provide stability. The filament has a core portion and a sheath portion having a lower melting point than the core portion. The sheath portion is thermally fusible to form a plurality of closed loops in which the respective sets of fibers are entrapped.
Although the reinforcement mat disclosed in WO 02/04725 solves many of the problems associated with past reinforcement mats, there continues to remain a need for improved reinforcement mats and methods for forming such improved reinforcement mats.